This invention relates to low intrinsic viscosity drop, low acetaldehyde, polyesters for producing packaging material such as bottles. More specifically, the polyesters contain additives such as fumed silicon dioxide. In another aspect, this invention relates to certain additives (micronized particles) for the polyesters and for polyamide polymers.
Polyethylene terephthalate is a polyester useful in preparing molded bottles to contain a wide variety of commercial liquids. The industry desires that the bottles have excellent strength and a high degree of clarity. The hollow blow molded thermoplastic, such as a thermoplastic polyester or a biaxially oriented polyethylene terephthalate resin, xe2x80x9cPETxe2x80x9d, container, is commonly used to contain food or beverage, has excellent physical properties, durability and a wide range of applications.
Heretofore, various compounds and catalysts have been used in the preparation of polyesters. Industry demands low intrinsic viscosity drop, low acetaldehyde, high clarity, neutral hue and low haze value that upon the normal reheat of a parison used in the blow molding of a polyester bottle, normal molding temperatures and the usual residence times will produce acceptable bottles. Industry, however, has had difficulty in providing the low intrinsic viscosity drop and low acetaldehyde, polyesters.
Industry continues to demand faster production speeds and improved heat rate, yet maintain the low intrinsic viscosity drop, low acetaldehyde, high clarity., neutral hue and low haze values of the polyester. In the past, production has used low levels of amorphous silicon dioxide to provide polyester bottles having a low tendency to stick together during and after molding. The bottles also have a reduced tendency to stick to other bottles during packing and transportation. The amorphous silicon dioxide is a non-crystalline silicon dioxide typically produced from a sol-gel process.
Another road block to industry""s demand for better processing are the twin crystallization peaks observed in polyester chips produced from batch or continuous polymerization plant, when a thermal scan is performed using a differential scanning calorimeter or similar instrument. In case of polyethylene terephthalate chips, the peaks range from 130xc2x0 to 150xc2x0 C. and from 160xc2x0 to 170xc2x0 C. The commercially produced chips require many hours of expensive storage/relaxation time so that the two peaks merge into one peak. If the freshly produced chips are processed further without providing adequate storage/relaxation time, operating problems such as fusion and distortion of chips occur.
This invention is a low intrinsic viscosity drop, low acetaldehyde, polyester resin for producing packaging material such as bottles. The polyester contains additives of fumed silicon dioxide, calcium carbonate or barium sulfate. These additives are added in small amounts for achieving the following benefits:
i) Lower I.V. (Intrinsic Viscosity) drop during the injection molding process.
ii) Lower levels of acetaldehyde in the resultant preforms/bottles.
I have achieved these properties without affecting the strain-hardening properties during the stretch-blow molding operation and without affecting the anti-blemishness in the final bottles.
These additives provide the faster line speeds that production needs. While the addition of carbon black in small quantities in the polyester resin for improving infrared absorption is already known, the further addition of fumed silicon dioxide and/or other additives additionally increases the infrared absorption of the polyester resin without worsening its color as happens with just the addition of carbon black.
In another aspect of this invention, I have discovered that incorporating certain additives such as silicon-dioxide in micronized form in polyester polymer (such as polyethylene terephthalate (PET), polytrimethyleneterephthalate (PTT), polybutyleneterephthalate (PBT) or nylon polymers (such as nylon-6, nylon-66, nylon-610 etc.) result in a number of benefits. The most important of these is to hasten the shifting of the higher crystallization peak from 160xcx9c170xc2x0 C. to 130xcx9c150xc2x0 C. in virgin and freshly produced polyethylene terephthalate polymer chips. This also results in the reduction of melt viscosity in the polyester polymer. Further, the reduction in final processing temperatures during their polymerization leads to lower electrical power consumption. The reduction in final process temperatures during the polymerization of polyester and nylon results in production of chips with less potential to generate acetaldehyde in subsequent steps of production of preforms and bottles. Also, the bulk produced in draw textured synthetic filament yarn form polyester and nylon would be better stabilized since their rate of thermal crystallization is faster.